1. Field
Example embodiments relate to an image sensor including a microlens, an image sensor including the microlens, a method of forming the microlens and a method of manufacturing the image sensor. Other example embodiments relate to a method of forming a microlens which increases an optical efficiency, a microlens capable of increasing optical efficiency, an image sensor including the microlens and a method of manufacturing the image sensor.
2. Description of the Related Art
Microlenses are used in a variety of fields (e.g., image sensors, liquid crystal display (LCD) devices and optical communications systems). Microlenses can be used as an objective lens to record or reproduce information with respect to an optical disk drive (ODD) (e.g., a compact disk (CD) or digital versatile disk (DVD)).
An image sensor including a microlens is a semiconductor device used to convert an optical image to an electric signal. The conventional image sensor with the microlens may include a charge coupled device (CCD) and a complimentary metal oxide semiconductor (CMOS) image sensor.
The CCD has a plurality of MOS capacitors arranged in proximity to each other. The CCD operates by storing electric charges (carriers) generated by light in the MOS capacitors or by the movement of electric charges between the MOS capacitors. The CMOS image sensor utilizes CMOS technology wherein a control circuit and a signal processing circuit function as a peripheral circuit. The CMOS image sensor includes a plurality of unit pixels and a CMOS circuit that controls the output signals of the unit pixels.
FIG. 1 is a diagram illustrating a partial cross-sectional view of a conventional CMOS image sensor.
Referring to FIG. 1, the conventional CMOS image sensor includes an isolation layer (not shown) defining an active area on a semiconductor substrate SUB and a photodiode PD between the device isolation layers. The photodiode PD receives incident light and stores electric charges.
A first interlayer dielectric film ILD1 is formed on the surface of the semiconductor substrate SUB where the device isolation layer and the photodiode PD are formed. Although not illustrated, the first interlayer dielectric film ILD1 may be formed in a multi-layer structure. A metal wiring M, forming a unit pixel, is provided (or formed) in the first interlayer dielectric film ILD1. The metal wiring M is provided (or formed) such that it does not block the light incident on the photodiode PD. The metal wiring M may be formed in a multi-layer structure.
A color filter layer CF, having sections dyed in red, green and/or blue, is formed on the first interlayer dielectric film ILD1 over the photodiode PD. A second interlayer dielectric film ILD2 is formed on the color filter layer CF and a portion of the first interlayer dielectric film ILD1. The second interlayer dielectric film ILD2 functions as an overcoat layer to overcome step and/or adjust the focal length of a microlens.
A round-type microlens ML is formed on the second interlayer dielectric film ILD2 over the photodiode PD. The microlens ML functions by concentrating the incident light on the photodiode PD.
Although not illustrated, a protection film may be further provided on the first interlayer dielectric film ILD1 to protect the photodiode PD and metal wiring M from the degradation due to the intrusion of external moisture. A planarization layer may be provided on the protection layer to overcome step and/or increase adhesiveness.
In the conventional image sensor, the optical efficiency is degraded because a dead zone (an area where light cannot be concentrated) exists between the microlenses. The dead zone is generated during the formation of the microlens as described below.
FIGS. 2A through 2C are diagrams illustrating cross-sectional views of a method of forming a conventional microlens.
Referring to FIG. 2A, an interlayer dielectric film ILD, which functions as an overcoat layer, is formed on a semiconductor substrate (not shown) having a desired lower structure (not shown). A photoresist layer PR is coated over the interlayer dielectric film ILD.
Referring to FIG. 2B, a desired area of the photoresist layer PR (e.g., an area other than an area for forming a microlens) is exposed. The area is developed with a developer to form a photoresist pattern PRP.
Referring to FIG. 2C, the photoresist pattern PRP is allowed to reflow at a temperature greater than a glass transition temperature Tg (e.g., 120° C.-200° C.) to form a round-type microlens ML.
As described above, the microlens ML may be formed in a reflow process using photoresist. Due to the limits in resolution of exposure equipment, it is difficult to decrease the area between the photoresist pattern PRP less than a predetermined value. As the area between neighboring microlens ML increases, a dead zone forms.
In the conventional image sensor, the light concentration of the microlens ML is degraded if the incident light is inclined. If the incident light is input inclined, then a portion of the incident light passing through the microlens ML may not reach the photodiode PD corresponding thereto, causing the image sensor to malfunction.